#back-ground {
    height: 100vh;
    background-color: #292961;
    /*主页屏幕的首页图片*/
    /*background-image: url("https://tse3-mm.cn.bing.net/th?id=OIF-C.%2fupJ6Mke6NjuVjajfKNXGg&rs=1&pid=ImgDetMain");*/
    background-repeat: no-repeat;
    background-position: center center;
    background-size: cover;
    width: 100vw;
    color: white; /*字体颜色*/
    text-align: center;
}